Optical Reticle Load Port

ABSTRACT

An apparatus configured to load or unload a mask pod includes a first load port supporter and a second load port supporter spaced apart from the first load port supporter. Each of the first load port supporter and the second load port supporter includes at least portions of an L-shaped rectangular prism. The first load port supporter and the second load port supporter are disposed diagonally around a rectangular area, where first inner sidewalls of the first load port supporter and second inner sidewalls of the second load port supporter delimit boundaries of the rectangular area, and where a first width of the rectangular area is equal to a second width of the mask pod, and a first length of the rectangular area is equal to a second length of the mask pod.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.15/665,125, filed on Jul. 31, 2017, and entitled “Optical Reticle LoadPort,” which application is incorporated herein by reference in itsentirety.

BACKGROUND

Photolithography generally refers to an optical process used to transfergeometric patterns onto a substrate or a layer over a substrate. Manyphotolithography techniques use a light-sensitive material (commonlyreferred to as a “photoresist”) to create geometric patterns. Forexample, a photomask, or a reticle, may be disposed over thephotoresist, which may then be exposed to a radiation beam such asultraviolet (UV) or an excimer laser. A bake or cure operation may beperformed to harden the photoresist, and a developer may be used toremove either the exposed or unexposed portions of the photoresistdepending on whether a positive or negative resist is used. Thus, apattern corresponding to the pattern of the reticle is formed in thephotoresist, which may be used as a mask layer to transfer the patternto an underlying layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A and 1B illustrate a perspective view and a plan view of a loadport, respectively, in accordance with some embodiments.

FIGS. 2A and 2B illustrate a mask pod in an open state and in a closedstate, respectively, in accordance with some embodiments.

FIG. 3 is a cross-sectional view illustrating unloading of a mask podfrom a load port, in accordance with some embodiments.

FIG. 4 illustrates a perspective view of a load port with load portsupporters attached thereto, in accordance with some embodiments.

FIGS. 5A and 5B illustrate a perspective view and a plan view,respectively, of the load port supporter in FIG. 4, in accordance withsome embodiments.

FIG. 6 illustrates a perspective view of another load port supporter, inaccordance with some embodiments.

FIG. 7 illustrates a perspective view of a load port comprising loadport supporters, in accordance with some embodiments.

FIG. 8 illustrates a perspective view of the load port supporter shownin FIG. 7, in accordance with some embodiments.

FIG. 9 illustrates a perspective view of another load port supporter, inaccordance with some embodiments.

FIG. 10 illustrates a perspective view of a smart load port withsensors, in accordance with some embodiments.

FIG. 11 illustrates a perspective view of a smart load port withsensors, in accordance with some embodiments.

FIGS. 12-15 are cross-sectional views illustrating a method fordetecting an abnormal condition of the mask pod using a smart load port,in accordance with some embodiments.

FIGS. 16-17 illustrate various designs for locking devices of the smartload port, in accordance with some embodiments.

FIGS. 18A and 18B are cross-sectional views illustrating a method fordetecting an abnormal condition of the mask pod using a smart load port,in accordance with some embodiments.

FIGS. 19A and 19B are cross-sectional views illustrating a method fordetecting an abnormal condition of the mask pod using a smart load port,in accordance with some embodiments.

FIGS. 20A and 20B are cross-sectional views illustrating a method fordetecting an abnormal condition of the mask pod using a smart load port,in accordance with some embodiments.

FIGS. 21A and 21B are cross-sectional views illustrating a method fordetecting an abnormal condition of the mask pod using a smart load port,in accordance with some embodiments.

FIG. 22 illustrates the cross-sectional view of a load port havingsensors in both the load port supporter and on the upper surface of abase of the load port, in accordance with some embodiments.

FIGS. 23A-23B illustrate a design for locking devices used in the smartload port, in accordance with some embodiments.

FIGS. 24A-24B illustrate a design for locking devices used in the smartload port, in accordance with some embodiments.

FIG. 25 is a flow chart of a method for removing a mask pod from a loadport, in accordance with some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly. Throughout the presentdisclosure, unless otherwise specified, similar numbers are used todescribe similar parts.

Embodiments of the present disclosure are discussed in the context ofload port design and removing of a mask pod from the load port.Disclosed embodiments include load port supporters that are attached toa load port, or are used standalone. Sensors and locking devices areembedded in the disclosed load ports. Based on the outputs of thesensors, a control unit detects abnormal conditions of the mask pod, andactivates the locking devices to limit the movement of the mask pod andto prevent damage to the reticle carried by the mask pod.

FIG. 1A illustrates a perspective view of a load port 100 for loadingand unloading reticles (not shown) used in a photolithography tool forsemiconductor manufacturing. As illustrated in FIG. 1A, the load port100 has a shape of a rectangular ring with chamfers 103, which chamfers103 are between an upper surface 101 of the load port 100 and interiorsidewalls 105 of the load port 100. The chamfers 103 may also bereferred to as beveled edges in the present disclosure.

The load port 100 is made of a rigid material, such as steel, oraluminum titanium alloy, to maintain a pre-determined dimension thatmatches a dimension of a mask pod that will be loaded into the load port100. The surfaces of the load port 100 may be coated with a coatingmaterial to provide resistance to scratching. The coating material maycomprise chromium, or tungsten. For example, the coating material mayreduce or prevent particles of the material of the load port 100 frombeing scraped off (e.g., by the mask pod during loading and unloading)and contaminate the reticles carried in the mask pod.

In some embodiment, a width W₁ of the load port 100 is in the range ofabout 235 mm to about 255 mm. A length L₁ of the load port 100 may be inthe range of about 255 mm to 465 mm. A height H₁ of exterior sidewalls107 is in the range of about 15 mm to about 25 mm, and a height H₂ ofthe interior sidewalls 105 is in the range of about 10 mm to 15 mm, insome embodiments.

FIG. 1B illustrates a plan view of the load port 100 of FIG. 1A. Anopening 102 is in the middle of the load port 100. In the illustratedembodiment, the upper surface 101 of the load port 100 has a width W₂measured along the X-direction, and a width W₄ measured along theY-direction. In addition, an exterior sidewall 107A and a correspondinginterior sidewall 105A have a distance W₃ measured along theX-direction. Furthermore, an exterior sidewall 107B and a correspondinginterior sidewall 105B have a distance W₅ measured along theY-direction.

In some embodiments, the width W₂ is in a range from about 5 mm to about70 mm, and the width W₄ is in a range from about 50 mm to about 70 mm.The distance W₃ in a range from about 15 mm to about 85 mm, and thedistance W₅ is in a range from about 60 mm to about 85 mm, in someembodiments. A width W₆ of the opening 102 may be in a range from about215 mm to about 295 mm, and a length L₂ of the opening 102 may be equalto the width W₆. The above dimensions are merely non-limiting examples.Other dimensions are also possible and are fully intended to be includedwithin the scope of the present disclosure.

FIG. 2A and FIG. 2B illustrate side views of a mask pod 150 in an openstate and a closed state, respectively. Referring to FIG. 2A, the maskpad 150 has an upper portion (e.g., a cover) which is referred to as anupper mask pod 153, and a lower portion (e.g., a base) which is referredto as a lower mask pod 155. The upper mask pod 153 also has a handle151, which may be used by an operator (e.g., a human operator) to loadthe mask pod 150 into the load port 100 or to unload the mask pod 150from the load port 100 (see FIG. 3).

The lower mask pod 155 serves as a base to carry a reticle 160. Thelower mask pod 155 may have one or more supports 157, on which lies thereticle 160. The supports 157 may be made of a suitable material, suchas a material that is stiff, and resistant to heat and chemicalsencountered in semiconductor manufacturing environments, but not toohard to scratch the reticle. For example, polyetheretherketone (PEEK)may be used as the material for the supports 157.

FIG. 2B shows the mask pod 150 in closed state, where the lower mask pod155 is locked inside the upper mask pod 153 by a locking mechanism (notshown) of the mask pod 150. Under normal condition, duringtransportation (e.g., loading into and unloading from a lithographytool) of the reticle 160, the reticle 160 is carried inside the mask pod150, which is in the closed state, to prevent dust from falling onto thereticles 160 and/or to prevent damage (e.g., scratching) of the reticle160. In a plan view, the mask pod 150 may have a rectangular shape withdimensions matching the dimensions of the opening 102 (see FIG. 1B) ofthe load port 100.

FIG. 3 illustrates the loading of the mask pod 150 into, and/or theunloading of the mask pod 150 from, the load port 100, in someembodiments. In the discussion herein, “loading and unloading thereticle” is used interchangeably with “loading and unloading the maskpod,” since the reticle 160 is carrier by the mask pod 150 during theloading and the unloading operation.

As illustrated in FIG. 3, a movable base 110 of the load port 100,movable along an up-and-down direction 113, is docked with the load port110. To load the reticle 160 into a lithography tool, the mask pod 150is loaded onto the movable base 110 with the reticle 160 inside the maskpod 150. Thereafter, the movable base 110 moves downwards like anelevator, carrying the mask pod 150 into a lithography tool (not shown)disposed below the load port 100. Once inside the lithography tool, themask pod 150 is opened, and the reticle 160 is removed from the mask pod150 and used by the lithography tool for a photolithography processing.

After the photolithography process is finished, the reticle 160 isreturned into the mask pod 150, the mask pod 150 closes, and the movablebase 110 moves up like an elevator, carrying the mask pod 150 toward theload port 100. Once the movable base 110 docks with the load port 100,e.g., when the movable base 110 reaches the position illustrated in FIG.3, the mask pod 150 is removed from (e.g., out of) the load port 100,such that the reticle 160 can be removed and stored, and/or a newreticle can be loaded into the mask pod 150 for another photolithographyprocessing.

The unloading (e.g., removal) of the mask pod 150, may be doneautomatically by machines. However, during semiconductor manufacturing,abnormal conditions or emergencies may occur (e.g., loss of power), thenthe mask pod 150 may be removed by a human operator. In a properunloading procedure, the mask pod 15 should be removed out of the loadport 100 in a straight upward direction 115, e.g., a directionperpendicular to an upper surface of the movable base 110. However, whena human operator removes the mask pod 150 out of the load port 100, themask pod 150 may not travel in the straight upward direction 115.Instead, the mask pod 150 may travel along directions, such asdirections 117, that are not perpendicular to the upper surface of themovable base 110. In the present disclosure, a direction (e.g., 117)that is non-perpendicular to the upper surface of the movable base 110is also referred to as a non-perpendicular direction, and a movement(e.g., by the mask pod 150) along a non-perpendicular direction isreferred to as a non-perpendicular movement. Damage to the reticle 160,the mask pod 150, and/or the load port 100 may occur when the mask pod150 is removed from the load port 100 along non-perpendiculardirections, as will described in more details hereinafter.

The load port 100 has chamfers 103 which make it easy to fit the maskpod 150 into the openings 102 of the load port 100. The chamfers 103,however, reduce the height of the interior sidewalls of the load port100 to H₂. Since the interior sidewalls 105 of the load port 100 limitlateral movement of the mask pod 150, the chamfers 103 reduces theeffectiveness of the interior sidewalls 105 in terms of limiting lateralmovement of the mask pod 150. Once the mask pod 150 moves higher than H₂from the movable base 110, gaps between the chamfers 103 and the maskpod 150 allow for lateral movement of the mask pod 150, thus may resultin non-perpendicular movement of the mask pod 150 by a human operator.

In removal of the mask pod 150 along non-perpendicular directions,excessive contact between the mask pod 150 and the load port 100, suchas bumping or scratching, may occur, which may cause damage to the maskpod 150, load port 100, or even the reticle 160 inside the mask pod 150.In addition, loose particles from the scratches of the mask pod 150and/or load port 100 may pollute the reticle 160. Under certain abnormalconditions, the upper mask pod 153 may not lock securely with the lowermask pod 155, and may separate from the lower mask pod 155 during theremoval of the mask pod 150 from the load port 100. If separation of theupper mask pod 153 from the lower mask pod 155 happens when the mask pod150 is moving upward in the load port 100, the reticle 160 may fly outof the load port 100 due to a suction force generated by a tight fitbetween the load port 100 and the mask pod 150 and the upward movementof the upper mask pod 153, resulting in serious damage to the reticle160. The present disclosure addresses these issues with various designfeatures.

FIG. 4 illustrates a perspective view of a load port 200, in someembodiments. The load port 200 in FIG. 4 includes the load port 100 ofFIG. 1A, and two load port supporters 210 attached to two diagonal uppercorners of the load port 100. As illustrated in FIG. 4, a shape of theload port supporters 210 is substantially an L-shaped prism, with thebottom portions of the L-shaped prism modified to match the profile ofthe upper surface 101 and the chamfers 103 of the load port 100.

The load port supporters 210 are made of a rigid material, such assteel, aluminum titanium alloy, or polyether ether ketone (PEEK). Insome embodiment, a hardness of the load port supporters 210 is equal toor higher than a hardness of the load port 100. Having load portsupporters 210 with equal or higher hardness than the load port 100 mayreduce the chances of scratching the load port supporter 210 duringloading and unloading of the mask pod 150. The load port supporters 210are attached (e.g., fastened) to the load port 100 securely via anysuitable method, such as screws. The surface of the load port supporters210 may be coated with a coating material such as chromium or tungstento reduce or prevent scratching.

As illustrated in FIG. 4, each load port supporter 210 has two innersidewalls 211 and 213 that are flush with respective interior sidewalls105 of the load port 100. In a plan view, the four inner sidewalls(e.g., two inner sidewalls from each load port supporter 210) of the twoload port supporters 210 define (e.g., delimit) a rectangular area thatis the same as (e.g., overlaps) the opening 102 (see FIG. 1B) of theload port 100.

As illustrated in FIG. 4, the two load port supporters 210 increase theeffective height of the interior sidewalls of the load port 200 toH₁+H₃, where H₁ is the height of the exterior sidewalls of the load port100, and H₃ is a height between the upper surface 101 of the load port100 and the L-shaped top surface of the load port supporter 210.Therefore, lateral movement (e.g., a non-perpendicular movement) of themask pod 150 is reduced or prevented for a longer distance (e.g.,H₁+H₃). Since the mask pod 150 has to travel upward for a longerdistance (e.g., H₁+H₃), in the event of a separation of the upper maskpod 153 from the lower mask pod 155, it is less likely that the reticle160 will fly out of the load port 200, thus reducing the chances ofserious damage to the reticle 160.

FIG. 5A and FIG. 5B illustrate a perspective view and a plan view of theload port supporter 210 of FIG. 4, respectively. As illustrated in FIG.5A, the shape of the load port supporter 210 comprises an L-shapedrectangular prism, with a first bottom extension 221 and a second bottomextension 223 attached to a bottom surface 217 (shown as an edge in FIG.5A) of the load port supporter 210. In other words, without the firstbottom extension 221 and without the second bottom extension 223, theload port supporter 210 in FIG. 5A would have a shape of an L-shapedprism, which L-shaped prism has an L-shaped upper surface 215, anL-shaped bottom surface 217, and six rectangular sidewalls. With thefirst bottom extension 221 and the second bottom extension 223, however,the sidewall 225 and the sidewall 235 of the load port supporter 210have shapes that are a combination of a rectangular and a triangle, andthe other four sidewalls (e.g., 211 and 213) still have rectangularshapes. In addition, two slanted surfaces 219 and 229 are added to thesurfaces of the load port supporter 210, resulting a total of tensurfaces (e.g., a top surface, a bottom surface, six sidewalls, and twoslanted surfaces) for the load port supporter 210.

As illustrated in FIG. 5A, the first bottom extension 221 is below thebottom surface 217, and a cross-section of the first bottom extension221 along sidewall 225 has a shape of a triangle, which triangle isbelow the dashed line illustrated on the sidewall 225. A slanted surface219 (shown as an edge in FIG. 5A) of the first bottom extension 221forms an angle α with the bottom surface 217 of the load port supporter210. The angle α may be between 90 degrees to about 180 degrees, such as135 degrees. In some embodiments, the angle α is equal to an anglebetween the upper surface 101 and the chamfer 103 of the load port 100(see FIG. 4). Since the bottom surface 217 and the slanted surface 219of the load port supporter 210 contact the upper surface 101 and thechamfer 103 of the load port 100, respectively, having the angle αmatching the angel between the upper surface 101 and the chamfer 103will ensure a good fit between the load port supporter 210 and the loadport 100. Similarly, the second bottom extension 223 also has atriangular cross-section at the sidewall 235. In addition, a slantedsurface 229 of the second bottom extension 223 and the bottom surface217 form the angle α. In some embodiments, a height H₃ (see FIG. 5A) ofthe load port supporter 210, measured between the upper surface 215 andthe bottom surface 217, is in a range from about 30 mm to about 100 mm.

FIG. 5B shows the plan view of the load port supporter 210, with thefirst bottom extension 221 and the second bottom extension 223illustrated in phantom. Referring to FIG. 5B, the upper surface 215 ofthe load port supporter 210 has a width W3′ between an outer sidewall220 and the inner sidewall 211, and a width W5′ between an outersidewall 224 and the inner sidewall 213. In addition, the bottom surface217 of the load port supporter 210 has a width W2′ between the outersidewall 220 and the slanted surface 219, and a width W4′ between theouter sidewall 224 and the slanted surface 229.

In some embodiments, the width W₃′ is in a range from about 15 mm and toabout 55 mm. The width W₅′ may be in a range from about 40 mm to about60 mm. The width W₂′ may be in a range from about 5 mm to about 50 mm,and the width W₄′ may be in a range from about 30 mm to about 50 mm. Insome embodiments, the width W₃′ and the width W₅′ are the same as thewidth W₃ and the width W₅ illustrated in FIG. 1B, respectively. In someembodiments, the width W₂′ and the width W₄′ are the same as the widthW₂ and the width W₄ illustrated in FIG. 1B, respectively. A width W₈ ofthe inner sidewall 211 is in a range from about 50 mm to about 70 mm,and a width W₁₀ of the inner sidewall 213 is in a range from about 35 mmto about 55 mm.

FIG. 6 illustrates another load port supporter 210 that may be used inplace of, or with, the load port supporter 210 in FIG. 5A, in accordancewith an embodiment. The load port supporter 210 in FIG. 6 is similar tothe load port supporter 210 in FIG. 5A, but with the addition of twochamfers 231 between the upper surface 215 and the inner sidewalls211/213. Each chamfer 231 form an angle β with the upper surface 215 ofthe load port supporter 210. The angle β is the same as the angle αbetween the lower surface 217 and the slanted surface 219 of the firstbottom extension 221, in some embodiments, although the angle α may alsobe different from the angle β. By having the chamfers 231, it is easierto load the mask pod 150 into the load port 200.

In some embodiments, a width W₇ of the upper surface 215 of the loadport supporter 210 of FIG. 6 is in a range from about 30 mm to about 50mm, and a width W₉ of the upper surface 215 is in a range from about 5mm to about 50 mm. In some embodiments, the width W₇ and the width W₉are equal to the width W₂′ and the width W₄′ in FIG. 5B, respectively.

Although two load port supporters 210 are illustrated in FIG. 4, morethan two load port supporters, such as three, or four load portsupporters may be used. For example, one or two more additional loadport supporters 210 may be attached to the unoccupied upper corners(e.g., the bottom left and/or the top right corner in FIG. 4) of theload port 100. In embodiments where two load port supporters are used,the two load port supporters can be attached to any two diagonalcorners. For example, instead of the top left and the bottom rightcorner as illustrated in FIG. 4, the two load port supporters 210 may beattached to the bottom left and the top right corners of the load port100. These and other variations to the design of the load port 200 arefully intended to be included within the scope of the presentdisclosure.

FIG. 7 illustrates another load port 300 in accordance with anembodiment. In FIG. 7, the load port 300 comprises two load portsupporters 310, and the ring-shaped load port 100 (see FIG. 4) is notused in the load port 300. Each of the load port supporters 310 has ashape of an L-shaped rectangular prism. The material for the load portsupporters 310 may be similar to that of the load port supporters 210,details are not repeated here. A height H₄ of the load port supporter310 is larger than the height H₁ (see FIG. 4) of the load port 100,thereby providing more control of lateral movement of the mask pod 150to force a straight-up movement of the mask pod 150 during unloading. Ataller load port supporter 310 also reduces the risk of the reticle 160flying out of the load port 300 when separation of the upper mask podfrom the lower mask pod happens.

As illustrated in FIG. 7, the four inner sidewalls 311/313 of the twoload port supporters 310 defines (e.g., delimit) the boundary of arectangular area 302 with a width W₁₁ and a length L₃. The dimensions(e.g., L₃ and W₁₁) of the rectangular area 302 match the dimension ofthe mask pod 150, or the dimension of the opening 102 (see FIG. 1B) ofthe load port 100, in some embodiments. An advantage of the load port300 is that by adjusting the distances between the two load portsupporters 310, the same load port supporters 310 can be reconfigured toform load port 300 with different dimensions (e.g., L₃ and W₁₁) toaccommodate mask pod 150 with different sizes.

FIG. 8 shows a perspective view of the load port supporter 310illustrated in FIG. 7. In some embodiments, the height H₄ of the loadport supporters 310 is in a range from about 30 mm to about 50 mm. Otherdimensions of the load port supporter 310 may be similar tocorresponding dimensions of the load port supporter 210 in FIGS. 5A and5B, thus details are not repeated here.

FIG. 9 shows a perspective view of another load port supporter 310 thatmay be used in place of, or with, the load port supporter 310 in FIG. 8,in accordance with an embodiment. The load port supporter 310 in FIG. 9is similar to the load port supporter 310 in FIG. 8, but with twochamfers 329 between the upper surface 315 and two inner sidewalls 311and 313. The chamfers 329 facilitate loading of the mask pod 150 intothe load port 300.

Although two load port supporters 310 are illustrated in FIG. 7, morethan two load port supporters, such as three, or four load portsupporters may be used. For example, one or two more additional loadport supporters 310 may be disposed at the unoccupied corners (e.g., thebottom left and/or the top right corner in FIG. 7) of the rectangulararea 302. In embodiments where two load port supporters 310 are used,the two load port supporters 310 can be disposed at any two diagonalcorners. For example, instead of the top left and the bottom rightcorner as illustrated in FIG. 7, the two load port supporters 310 may bedisposed at the bottom left and the top right corners of the rectangulararea 302. These and other variations to the design of the load port 300are fully intended to be included within the scope of the presentdisclosure.

FIG. 10 illustrates a perspective view of a load port 400 in accordancewith an embodiment. The load port 400 is similar to the load port 200 inFIG. 4, but with a plurality of sensors (e.g., 401, 405) and lockingdevices (e.g., 403) embedded in the load port 400. In particular, foreach of the load port supporters 210 (e.g., 210A or 210B), a firstoptical sensor 401 is embedded in the inner sidewall 211 and/or theinner sidewall 213 of the load port supporter 210, and a second opticalsensor 405 is embedded in the interior sidewall(s) 105 of the load port100 and is disposed below the first optical sensor 401. Exteriorsurfaces of the optical sensors (e.g., 401 and 405) are flush with theinner sidewall 211 and/or the inner sidewall 213, or are recessed fromthe inner sidewall 211 and/or the inner sidewall 213, so that theoptical sensors (e.g., 401 and 405) do not interfere with the movement(e.g., up or down movement) of the mask pod 150 inside the load port400.

For each load port supporter 210, a locking device 403 is embedded inthe inner sidewall 211 and/or the inner sidewall 213, and is between thefirst optical sensor 401 and the second optical sensor 405. When thelocking device 403 is in a non-active state (e.g., locking device 403not deployed), exterior surfaces of the lock device 403 is flush withthe inner sidewall 211 and/or the inner sidewall 213, or are recessedfrom the inner sidewall 211 and/or the inner sidewall 213, so that thelocking device 403 does not interfere with the movement of the mask pod150 inside the load port 400. When the locking device 403 is in anactive state (e.g., locking device 403 deployed), the locking device403, or portions of it, protrudes into the opening 102 of the load port400 to limit (e.g., block) the movement of the mask pod 150 inside theload port 400, details of which will be discussed hereinafter.

Still referring to FIG. 10, each of the optical sensors 401/405 in theload port supporter 210A form a pair of optical sensors withcorresponding optical sensors 401/405 (not visible in the perspectiveview of FIG. 10) in the load port supporters 210B. For example, thefirst optical sensor 401 in the load port supporter 210A may be anoptical transmitter, and the first optical sensor 401 in the load portsupporter 210B may be an optical receiver, or vice versa. Therefore, thetwo corresponding optical sensors (e.g., the optical sensor 401 in 210Aand the optical sensor 401 in 210B) form a pair of optical sensors fortransmitting (by one optical sensor) and receiving (by the other opticalsensor) optical signals. The present disclosure allows great flexibilityin assigning the locations (e.g., in 210A or in 210B) of the opticaltransmitter and the optical receiver in a pair. For example, the opticalsensors 401/405 in load port supporter 210A may both be opticaltransmitters. As another example, the optical sensors 401/405 in theload port supporter 210A may both be optical receivers. As yet anotherexample, the optical sensors 401/405 in the load port supporter 210A mayinclude an optical transmitter and an optical receiver.

The optical sensors 401/405 may transmit or receive laser signals,infra-red (IR) signals, or other directional signals, such that thesignals transmission between a pair of optical sensors would notinterfere with signals transmission between another pair of opticalsensors. For example, laser signals may be used to establish alight-of-sight (LOS) communication channel between a pair of opticalsensors. The signals received by the receiving optical sensor will beprocessed to detect an abnormal condition of the mask pod, and to deploythe locking device 403 to prevent damage to the reticle, as will bediscussed in more details hereinafter with reference to FIGS. 12-17.Through the present disclosure, load ports with sensors may also bereferred to as smart load ports.

The load port supporter 210 shown in FIG. 10 may be have chamfers formedbetween the upper surface 215 and the inner sidewalls 211/213, similarto the chamfers 231 in FIG. 6. The optical sensors 401/405, and thelocking device 403 are illustrated in FIG. 10 as being embedded in bothinner sidewalls 211 and 213 of the load port supporter 210. Depending onthe size of the optical sensors 401/405 and the size of the lockingdevice 403, the optical sensors 401/405 and/or the locking device 403may be embedded in one of the inner sidewalls (e.g., 211 or 213), or maybe embedded along the edge where the two inner sidewalls 211 and 213intersect with each other. In addition, the second optical sensor 405 isillustrated as being embedded in the interior sidewall 105 of the loadport 100, however, the second optical sensor 405 may also be embedded inthe inner sidewall 211 and/or the inner sidewall 213 of the load portsupporter 210. Furthermore, the locations (e.g., the distance betweenthe optical sensor 401/405, the locking device 403, and a bottom surfaceof the load port 100) of the optical sensors 401/403 and/or the locationof the locking device 403 may be changed according to various factorssuch as the size of the mask pod 150, size of the load port 100, and thesize of the load port supporter 210. These and other variations to thedesign of the load port 400 are fully intended to be included within thescope of the present disclosure.

FIG. 11 illustrates a perspective view of a smart load port 500 inaccordance with an embodiment. The smart load port 500 is similar to theload port 300 illustrated in FIG. 7, but with optical sensors 501/505and locking devices 503 embedded in the inner sidewalls 311/313 of theload port supporters 310. In particular, for each load port supporter310, a first optical sensor 501, a locking device 503, and a secondoptical sensor 505 are embedded in the inner sidewall 311 and/or theinner sidewall 313 of the load port supporter 310, with the lockingdevice 503 between the first optical sensor 501 and the second opticalsensor 505. Corresponding optical sensors in the pair of load portsupporters, e.g., a first optical sensor 501 in load port supporter 310Aand a first optical sensor 501 (not visible in FIG. 11) in load portsupporter 310B, form a pair of optical sensors. In the example of FIG.11, two pairs of optical sensors (e.g., 501 in 310A and 501 in 310B, 505in 310A and 505 in 310B) are formed. Each pair of the optical sensorsinclude an optical transmitter and an optical receiver. Directionalsignals (e.g., laser, IR) are used to maintain a directionalcommunication link between each pair of optical sensors withoutinterfering with the other pair(s) of optical sensors. Details of theoptical sensors 501/505 and locking device 503 are similar to those ofoptical sensors 401/405 and locking device 403 in FIG. 10, respectively,thus details are not repeated here.

Modification to the load port 500 are possible. For example, chamfersmay be formed between the upper surface 315 and the inner sidewalls311/313 of the load port supporters 310, similar to the chamfers 329 inFIG. 9. Locations of the optical sensors 501/505 and locking device 503may be adjusted according to various factors such as the size of themask pod 150, and the size of the load port supporter 310. These andother variations to the design of the load port 500 are fully intendedto be included within the scope of the present disclosure.

FIGS. 12-15 illustrate a method of removing a mask pod from a smart loadport, in some embodiments. The smart load port 500 of FIG. 11 is used asan example in the illustrated embodiment, with the understanding thatother smart load port, such as the smart load port 400 of FIG. 10, mayalso be used without departing from the spirit of the presentdisclosure.

FIG. 12 shows the cross-sectional views of the smart load port 500, themovable base 110 of the smart load port 500, and the mask pod 150. Forsimplicity, the lower mask pod and the reticle carried inside the maskpod 150 are not shown. FIG. 12 shows a control unit 180 coupled tooptical sensors 501A/505A and a locking device 503A in load portsupporter 310A. The control unit 180 is also coupled to optical sensors501B/505B and a locking device 503B in load port supporter 310B. Thecontrol unit 180 may be a micro-controller, a central processing unit(CPU), an application specific integrated circuit (ASIC), or othersuitable controller. The coupling between the control unit 180 and theoptical sensors 501/505 and the locking devices 503 may be through wires(e.g., copper wire, coaxial cable, optical fiber) or through wirelesschannels (e.g., WiFi, Bluetooth, or other standard or proprietarywireless protocols). For simplicity, the control unit 180 and thecoupling between the control unit 180 and the optical sensors 501/505and the locking devices 503 are not shown in FIGS. 13-17, with theunderstanding that the control unit 180 and the coupling are stillpresent in FIGS. 13-17.

Without loss of generality, solely to facilitate the discussion below,the optical sensors 501A and 505A in the load port supporter 310A areassumed to be optical transmitters, and the optical sensors 501B and505B in the load port supporter 310B are assumed to be opticalreceivers.

Referring to FIG. 12, at the beginning of the unloading process, themask pod 150, with the reticle 160 (not shown) inside, is on the movablebase 110 and is ready to be removed from the smart load port 500. Thecontrol unit 180 instructs the optical transmitters 501A and 505A totransmit optical signals, and checks the output of the optical receivers501B and 505B. Since the mask pod 150 is between the first pair ofoptical sensors 501A/501B and the second pair of optical sensors505A/505B, the transmitted optical signals are blocked by the mask pod150, and the outputs of the optical receivers 501B/505B indicate that nooptical signal is received at 501B and 505B. Using a notation of “1” and“0” to indicate respectively “optical signal received” and “no opticalsignal received,” and using a binary two-bit word [B₁B₀] to representthe outputs from the optical receivers 501B/505B, with bits B₁ and B₀corresponding to the outputs of the optical receivers 501B and 505B,respectively, the outputs of the optical receivers 501B/505B in FIG. 12are represented by a two-bit word [00]. The value of the two-bit word[B₁B₀] is also referred to as the state of the optical receivers501B/505B. Following the convention of treating bit B₁ as the mostsignificant bit (MSB) of the two-bit word and bit B0 as the leastsignificant bit (LSB) of the two-bit word, the state of the opticalreceivers 501B/505B in FIG. 12 is 0.

Next, as illustrated in FIG. 13, the mask pod 150 is moving upward andclears (e.g., move above) the communication path between the second pairof optical receiver 505A/505B, but still blocks the communication pathbetween the first pair of optical receivers 501A/501B. As a result, theoutput of the second optical receiver 505B indicates “optical signalreceived,” while the output of the optical receiver 501B indicates“optical signal not received.” Therefore, the outputs of the opticalreceivers 501B/505B in FIG. 13 are represented by a two-bit word [01],and the state of the optical receivers 501B/505B in FIG. 13 is 1.

Next, as illustrated in FIG. 14, the mask pod 150 moves further upwardand clears the communication path between both the first pair of opticalsensors 501A/501B and the second pair of optical sensors 505A/505B. As aresult, the output of first optical receiver 501B and output of thesecond optical receiver 505B both indicate “optical signal received.”Therefore, the outputs of the optical receivers 501B/505B in FIG. 14 arerepresented by a two-bit word [11], and the state of the opticalreceivers 501B/505B in FIG. 14 is 3.

FIGS. 12-14 illustrate the normal operating conditions for unloading themask pod 150 from the smart load port. Therefore, the state of theoptical receivers 501B/505B, as illustrated in FIGS. 12-14, changes inthe following sequence: 0→1→3.

FIG. 15 illustrate an abnormal condition of the mask pod 150, where theupper mask pod 153 separated from the lower mask pod 155 during removalof the mask pod 150. As illustrated in FIG. 15, after being separatedfrom the upper mask pod 153, the lower mask pod 155 and the reticle 160are left on the movable base 110 as the upper mask pod 153 travelsupward and clears (e.g., not blocking) the communication path betweenthe first pair of optical sensors 501A/501B. The communication pathbetween the second pair of optical sensors 505A/505B are blocked by thelower mask pod 155. Therefore, the outputs of the optical receivers501B/505B changes from [0 0] to [1 0] as the upper mask pod 153 travelsupwards, in some embodiments. In other words, the state of the opticalreceivers 501B/505B under the abnormal condition changes in thefollowing sequence: 0→2 in the illustrate embodiment. Note that thestate 2 for the optical receivers 501B/505B does not appear in normalcondition, and therefore, could be used by the control unit 180 todetect the abnormal condition. In some embodiments, the control unit 180determines that an abnormal condition occurred of the mask pod 150 whenthe state of the optical receivers 501B/505B is 2.

In some embodiments, the control unit 180 monitors the transition of thestate of the optical receivers 501B/505B (e.g., 0→1→3, or 0→2), and byanalyzing the sequence of state, may determine more details regarding,e.g., how and when an abnormal condition occurred. For example, if thelower mask pod 155 initially moved above the second pair of opticalsensors 505A/505B before being separated from the upper mask pod 153 andfalling back onto the movable base 110, the sequence of state may showthe following transition: 0→1→0→2. The control unit 180 may continuouslymonitor (e.g., sample the output of the optical receivers 501B/505B at asampling frequency throughout the unloading process) the state of theoptical receivers 501B/505B. The time stamp of the samples of theoutputs of the optical receivers may provide the time when an abnormalcondition (e.g., separation of the upper mask pad from the lower maskpod) happened. A reconstruction of the abnormal condition with detailedtiming information may be possible by using the samples of the output ofthe optical receivers 501B/505B. Such a reconstruction may be used toimprove operation procedures and to prevent future occurrence of theabnormal condition.

In some embodiments, in response to the detection of the abnormalcondition, the control unit 180 activates, or deploys, the lockingdevice 503A/503B. When activated, the locking devices 503A/503B protrudefrom the sidewalls of the load port supporter 310 into the spacedelimited by the inner sidewalls 311/313 (see FIG. 11) of the load portsupporter 310. In some embodiments, the activated locking devices503A/503B limit the movement of the lower mask pod 155, e.g., preventingit from moving upward passing the locking devices 503A/503B, therebyreducing the chance of the reticle 160 getting out of the load port 310and being damaged. Warning signals, such as warning lights or alarm, maybe triggered by the control unit 180, so that the abnormal condition maybe handled and resolved properly by the operator.

In the example of FIG. 15, a distance S₁ between the locking device 503Aand 503B is larger than a width S₂ of the reticle 160, but smaller thana width S₅ of the lower mask pod 155. Therefore, in limiting themovement of the lower mask pod 155, the locking devices 503A/503B maycontact the lower mask pod 155 but may not contact the reticle 160.

FIG. 16 and FIG. 17 illustrate two more examples of the locking devices503 limiting the movement of the lower mask pod 155 and/or the reticle160 under abnormal condition of the mask pod 150. FIG. 16 and FIG. 17are similar to FIG. 15, but with different shapes and/or dimensions forthe locking devices 503.

In FIG. 16, the distance 51 between the locking device 503A and 503B issmaller than the width S₂ (see FIG. 15) of the reticle 160, and is alsosmaller than the width S₅ (see FIG. 15) of the lower mask pod 155.Therefore, in limiting the movement of the lower mask pod 155, thelocking devices 503A/503B may contact the reticle 160. This design mayensure that the reticle 160 will not move above the locking devices 503and get out of the load port 310. The material of the locking device503, or the portion of the locking device 503 that contacts the reticle160, may be a suitable material (e.g., PEEK) to avoid scratching thereticle 160.

In FIG. 17, the locking devices 503A/503B has a step shape in across-sectional view. In particular, each locking device 503 comprise afirst portion 507 and a second portion 509. The bottom surface of thesecond portion 509 is closer to the lower mask pod 155 than the bottomsurface of the first portion 507. A distance S₃ between the firstportions 507 of the locking devices 503A/503B is smaller than the widthW₅ (see FIG. 15) of the reticle 160, and a distance S₄ between thesecond portions 509 are larger than the width W₅ of the reticle 160.Therefore, in limiting an upward movement of the lower mask pod 155, thesecond portion 509 may contact the lower mask pod 155, and the firstportion 507 may contact the reticle 160.

Still referring to FIG. 17, in some embodiments, an offset H5 betweenthe bottom surface of the first portion 507 and the bottom surface ofthe second portion 509 is equal to or larger than a distance H6 betweenthe upper surface of the reticle 160 and the upper surface of the lowermask pod 155. This design may ensure that in limiting an upward movementof the lower mask pod 155 and the reticle 160, the bottom surface of thesecond portion 509 makes contact with the lower mask pod 155 at a sametime as, or earlier than, the moment that the bottom surface of thefirst portion 507 makes contact with the reticle 160. Therefore, thefull force of impact between the blocking devices 503 and the lower maskpod 155/reticle 160 is not absorbed by the reticle 160 alone. Instead,the lower mask pod 155 may absorb most of the impact force if H₅ islarger than H₆, or the lower mask pod 155 and the reticle 160 may sharethe impact force if H₅ is equal to H₆. By lowering the impact forceexperienced by the reticle 160, the design in FIG. 17 reduces the chanceof the reticle 160 being damaged when the locking devices 503 aredeployed. To further reduce the chance of damages to the reticle 160,the first portion 507 may be made of a material that is softer than thatof the second portion 509. For example, the first portion 507 may bemade of aluminum titanium alloy or PEEK, and the second portion 509 maybe made of steel or aluminum titanium alloy. In other embodiments, thefirst portion 507 and the second portion 509 are made of a samematerial.

FIGS. 18A-21B illustrate various embodiments of method to preventnon-perpendicular movement of the mask pod 150 during the unloadingprocess using smart load ports. Referring to FIG. 18A, cross-sectionalviews of a smart load port comprising load port supporters 350 (e.g.,350A and 350B), the movable base 110, and sensors 112/114 are shown.Each of the load port supporters 350 has a locking device 503 (e.g.,503A or 503B) built in. FIG. 18A also shows the movable base 110, whichmay be configured to move the mask pod 150 in and out of a lithographytool (not shown). On the upper surface of the movable base 110 are twosensors 112 and 114 proximate a left end and a right end of the movablebase 110. The sensors 112 and 114 are configured to detect the positionof the mask pod 150, e.g., as the mask pod 150 is being lifted up fromthe movable base 110. The sensors 112/114 and the locking devices 503are coupled to a control unit 180. The control unit 180 monitors theoutput of the sensors 112/114 in real-time, and determines whether themask pod 150 is being lifted up along the straight upward direction 115in real-time. When the sensors 112/114 detect that the mask pod 150 isin a titled position (e.g., being lifted up in a non-perpendiculardirection), the control unit 180 deploys the locking device 503 to limitthe movement (e.g., stopping the mask pod 150) of the mask pod 150 torectify the situation.

The sensors 112 and 114 may be any suitable sensors that could detectthe position of the mask pod 150. In the example of FIG. 18A, thesensors 112 and 114 are two pressure sensors. In some embodiments, whenthe mask pod 150 is lying flat on the movable base 110, the outputs ofthe sensors 112 and 114 are substantially equal. Minor differencesbetween the outputs (e.g., pressure values) of the sensors 112 and 114may occur even when the mask pod 150 is lying flat on the movable base110 due to, e.g., sensitivity differences between sensors 112 and 114.These minor differences between the outputs of the sensors 112 and 114,however, are small and within a pre-determined threshold. Thepre-determined threshold may be determined by, e.g., analyzing andcharacterizing the sensitivity difference between the sensors 112 and114, or by measuring the outputs of the sensors 112 and 114 throughrepeated experiments and heuristically determine the distribution of theoutput differences. The control unit 180 determines that the mask pod150 is in a flat position (e.g., the bottom surface of the mask pod 150is parallel to the upper surface of the movable base 110) when themagnitude of the difference between the outputs of the sensors 112 and114 are within the pre-determined threshold, in some embodiments. Anon-zero pre-determined threshold may help to reduce false alarm (e.g.,incorrect detection of a titled position for the mask pod 150).

FIG. 18B shows that the mask pod 150 is being lifted up from the movablebase 110 in a titled position (e.g., non-perpendicular direction). Thetiling of the mask pod 150 in FIG. 18B is exaggerated for illustrationpurpose. For simplicity, the control unit 180 and its coupling with thesensors 112/114 and the locking devices 503 are not shown in FIGS.18B-21B, with the understanding that the control unit 180 and thecoupling between the control unit 180 and the sensors and the lockingdevices are still present.

In FIG. 18B, the right side of the mask pod 150 is lifted up while theleft side of the mask pod 150 is still touching the movable base 110 andthe sensor 112. As a result, the output of the sensor 112 is larger thanthe output of the sensor 114, and the difference between the outputs ofthe sensors 112 and 114 may be larger than the pre-determined threshold.In some embodiments, the control unit 180 determines that anon-perpendicular movement of the mask pod 150 occurred when themagnitude of the difference between the outputs of the sensors 112 and114 is larger than the pre-determined threshold.

In response to the detection that the mask pod 150 is moving up in anon-perpendicular direction, the control unit 180 triggers deployment ofone or more locking devices 503. The locking device 503, upon beingdeployed, protrudes into the smart load port and stops thenon-perpendicular movement of the mask pod 150. Alarm signals such aslights or alarm sound may be triggered to warn the operator of thesituation, so that actions can be taken to rectify the situation. Bothlocking devices 503A and 503B are deployed to stop the mask pod 150 insome embodiments. In other embodiments, the control unit 180 determineswhich side (e.g., left side or right side) of the mask pod 150 istilting up based on the outputs of the sensors 112 and 114, and deploysone locking device 503, instead of two locking devices 503, to stop themask pod 150. For example, in the illustrated example, the right sidesensor 114 has a smaller output value (pressure value). Therefore, thecontrol unit 180 determines that the right side of the mask pod 150 istilting up, and thus, triggers deployment of the locking device 503B onthe right side to stop the mask pod 150.

FIGS. 19A and 19B illustrates a method to prevent non-perpendicularmovement of the mask pod 150 during the unloading process using smartload ports in accordance with another embodiment. The smart load portillustrated in FIGS. 19A and 19B is similar to that illustrated in FIGS.18A and 18B, but with different sensors 112 and 114. In particular, thesensors 112 and 114 in FIGS. 19A and 19B are sensors configured tomeasure a distance between a sensor and the mask pod 150, e.g., thedistance between the sensor and the bottom surface of the mask pod 150directly above the sensor. For example, the sensors 112 and 114 may beranger finders such as laser ranger finders or ultrasonic range finders.

In some embodiments, the sensor 112 (or 114) transmits a signal (e.g.,laser signal or ultrasonic signal) toward the mask pod 150, receives thesignal reflected by the mask pod 150, and measures the round trip timefor the transmitted signal to bounce back to the sensor 112 (or 114).The distance between the sensor 112 (or 114) and the mask pod 150 can bedetermined by the round trip time (or half of it) and the speed oftransmission of the transmitted signal. When the mask pod 150 is lyingflat on the movable base 110, the measured distances from both sensors112 and 114 are substantially equal. A pre-determined threshold for thedifferences between the output of the sensors 112 and 114 may bedetermined to account for factors such as sensitivity differencesbetween the sensors, and to reduce false alarm. Details regarding thepre-determined threshold may be similar to those discussed above withreference to FIG. 18A, thus are not repeated. In some embodiments, thecontrol unit 180 determines that the mask pod 150 is in a flat positionwhen the magnitude of the difference between the outputs of the sensors112/114 is within the pre-determined threshold.

Referring to FIG. 19B, when the mask pod 150 is being lifted up in anon-straight direction, the bottom surface of the mask pod 150 istitled. In the illustrated example, the output (e.g., distance value) ofthe sensor 114 on the right side is larger than the output of the sensor112 on the right side. In some embodiment, the control unit 180determines that a non-perpendicular movement of the mask pod 150happened when the magnitude of the difference between the outputs of thesensors 112 and 114 is larger than the pre-determined threshold. In someembodiments, both locking devices 503A and 503B are deployed in responseto the detection of the non-perpendicular movement of the mask pod 150.In other embodiments, one locking device (e.g., 503B) instead of twolocking devices (e.g., 503A and 503B) are deployed to stop the side ofthe mask pod 150 that is tilting up.

FIGS. 20A and 20B illustrates a method to prevent non-perpendicularmovement of the mask pod 150 during the unloading process using smartload ports in accordance with another embodiment. The smart load portillustrated in FIGS. 20A and 20B is similar to that illustrated in FIGS.18A and 18B, but with different sensors 112 and 114. In particular, thesensors 112 and 114 in FIGS. 20A and 20B are a pair of sensors that areconfigured to measure a travel time between the sensors 112 and 114 by atransmitted signal. For example, the sensor 112 may be an acoustictransmitter, and the sensor 114 may be an acoustic receiver, or viceversa.

In some embodiments, the control unit 180 calculates the travel timebetween the moment an acoustic signal 118 is transmitted by the acoustictransmitter (e.g., sensor 112) and the moment the transmitted acousticsignal arrives at the acoustic receiver (e.g., sensor 114). The acousticsignal travels along the interface between the mask pod 150 and themovable base 110, in some embodiments. Note that the speed of soundvaries in different media. Since the distance between the sensors 112and 114 is fixed, and the materials of the mask pod 150 and the movablebase 110 are known, the travel time T₁ when the mask pod 150 is lyingflat on the movable base 110 can be calculated or measured.

Referring to FIG. 20B, when the mask pod 150 is lifted up and tilted,e.g., with one side of the mask pod 150 still touching the movable base110, the path through which the acoustic wave travels includes some airgap. Since the speed of sound is much slower in the air than in a solidmaterial, the travel time T₂, when the mask pod 150 is tilted asillustrated in FIG. 20B, is larger than the travel time T₁. Theincreased travel time T₂, however, is smaller than a travel time T₃,when the mask pod 150 is lifted up in a straight upward direction (see115 in FIG. 3) and just off the movable base 110, in which case the paththrough which the acoustic wave travels includes more air gap. Thetravel time T₃ can be determined, e.g., heuristically throughmeasurements and experiments. Therefore, a travel time T₂ that is largerthan T₁ but smaller than T₃ may be used for detecting the condition thatthe mask pad 150 is being lifted up and tilted.

In some embodiments, the control unit 180 calculates the differencebetween T₂ and T₁, and compares the calculated difference with apre-determined threshold. The pre-determined threshold may bedetermined, e.g., heuristically through measurements and experiments.The pre-determined threshold may account for factors such as sensorsensitivity, and may be used to reduce false alarm (e.g., falsedetection of the tiling of the mask pod 150). In some embodiments, whenthe magnitude of the calculated difference (e.g., T₂−T₁) is smaller thanthe pre-determined threshold, the control unit 180 determines that themask pod 150 is in a flat position as illustrated in FIG. 20A. In someembodiments, when the magnitude of the calculated difference is largerthan the pre-determined threshold, and when T₂ is smaller than T₃, thecontrol unit 180 determines that a tilting (e.g., a non-perpendicularmovement) of the mask pod 150 is detected, and in response to thedetection of the tilting, the control unit 180 deploys the lockingdevices 503 to stop the mask pod 150 from going up further. In someembodiments, once the tilting of the mask pod 150 is initially detected,the control unit 180 waits for a predetermined amount of time andrepeats the operation described above for detecting the titling of themask pod 150, and if titling of the mask pod 150 is detected again, thecontrol unit 180 deploys the locking device 503. The delayed detectiondescribed above may further reduce the false alarm rate. Once detectionof the tilting of the mask pad 150 is confirmed, warning signals such aslights or alarm sound may be generated to alert the operator, so thatactions may be taken to rectify the situation. In some embodiments, bothlocking devices 503A and 503B are deployed in response to the detectionof the non-perpendicular movement of the mask pod 150.

FIGS. 21A and 21B illustrates a method to prevent non-perpendicularmovement of the mask pod 150 during the unloading process using smartload ports in accordance with another embodiment. The smart load portillustrated in FIGS. 21A and 21B is similar to that illustrated in FIGS.18A and 18B, but with different sensors. In particular, the sensors inFIGS. 20A and 20B include a first pair of sensors 112A/112B and a secondpair of sensor 114A/114B that are configured to measure a parameter thatis adjustable (e.g., affected) by pressure. For example, the first pairof sensors 112A/112B and the second pair of sensors 114A/114B may becurrent sensors. As illustrated in FIG. 21A, each pair of sensors (e.g.,112A/112B) are stacked together and disposed over the upper surface ofthe movable base 110. In some embodiments, each pair of sensors (e.g.,112A/112B) include two electrodes that are in contact with each other.As the pressure applied on the two electrodes change, the resistancebetween the two electrodes changes, which results in a change in thecurrent flowing through the electrodes. For example, when the pressureincreases, the two electrodes are pressed tighter together, resulting ina smaller resistance and larger current, and vice versa. The currentflowing through the electrodes is measured and becomes the output of thepair of sensors.

Referring to FIG. 21A, when the mask pod 150 is lying flat on themovable base 110, the measured current from the first pair of sensors112A/112B and the second pair of sensors 114A/114B are substantiallyequal. A pre-determined threshold for the differences between the outputof the first pair of sensors 112A/112B and the output of the second pairof sensors 114A/114B may be determined to account for factors such assensitivity differences between the sensors, and to reduce false alarm.Details regarding the pre-determined threshold may be similar to thosediscussed above with reference to FIG. 18A, thus are not repeated. Insome embodiments, the control unit 180 determines that the mask pod 150is in a flat position when the magnitude of the difference between theoutputs of first pair of sensors 112A/112B and the output of the secondpair of sensors 114A/114B is within the pre-determined threshold.

Referring to FIG. 21B, when the mask pod 150 is being lifted up in anon-straight direction, the bottom surface of the mask pod 150 istitled. In the illustrated example, the output (e.g., current value) ofthe second pair of sensors 114A/114B on the right side is smaller thanthe output of the first pair of sensors 112A/112B on the left side, dueto less pressure on the second pair of sensors 114A/114B. In someembodiment, the control unit 180 determines that a non-perpendicularmovement of the mask pod 150 happened when the magnitude of thedifference between the outputs of the first pair of sensors 112A/112Band the second pair of sensors 114A/114B is larger than thepre-determined threshold. In some embodiments, both locking devices 503Aand 503B are deployed in response to the detection of thenon-perpendicular movement of the mask pod 150. In other embodiments,one locking device (e.g., 503B) instead of two locking devices (e.g.,503A and 503B) is deployed to stop the side of the mask pod 150 that istilting up from moving upward.

In some embodiments, the first pair of sensors 112A/112B and the secondpair of sensors 114A/114B may be magnetic sensors, air flow sensors,water flow sensor, or the like. For example, a pipe with air flow orwater flow inside may be connected or coupled to a pair of sensors(e.g., 112A/112B, or 114A/114B). The pressure from the weight of themask pod 150 changes the air flow rate or water flow rate inside thepipe, which flow rate is then measured by the pair of sensors. Asanother example, the pressure from the weight of the mask pod 150 maychange a current value and/or a physical dimension of an electromagnetcoupled to the sensors, thus resulting in a change of the magnetic fieldof the electromagnet. The magnetic field is measured by the pair ofsensors. When the mask pod 150 is titled, the first pair of sensors112A/112B and the second pair of sensors 114A/114B produce differentmeasured values, and the difference between the measured values can beused to detect the non-perpendicular movement of the mask pod 150.

Variations and modifications to the disclosed embodiments are possible.For example, while two sensors (e.g., 501A and 505A in FIG. 12) areillustrated for each load port supporter (e.g., 310A in FIG. 12), morethan two sensors may be used. As another example, the method fordetecting abnormal condition discussed with reference to FIGS. 12-15 maybe combined with the method for detecting non-perpendicular movement ofthe mask pad 150 discussed with reference to FIGS. 18A-21B, asillustrated in FIG. 22. In the embodiment of FIG. 22, sensors 501/505,locking devices 503, and control unit 180 are similar to the sensors501/505, the locking device 503, and the control unit 180 in FIG. 12,respectively, and sensors 112 and 114 are similar to the sensors 112 and114 in FIGS. 18A-21B. The control unit 180 in FIG. 22 detects abnormalconditions of the mask pod 150 using outputs from the sensors 501, 505,112 and 114, and deploys the locking device(s) 503 in response to thedetection of an abnormal condition of the mask pod. These and othervariations and modifications are fully intended to be included withinthe scope of the present disclosure.

FIGS. 23A and 23B illustrate an embodiment of the locking device 503. Inparticular, FIG. 23A shows the locking device 503 in inactive mode, andFIG. 23B shows the locking device 503 in active mode (e.g., beingdeployed). When deployed, the locking device 503 extends outhorizontally. For example, the locking device 503 may have a telescopestructure and may be collapsed when not activated. When activated, thelocking device 503 telescopes out to limit (e.g., block) the movement ofthe mask pod 150.

FIGS. 24A and 24B illustrate another embodiment of the locking device503. In particular, FIG. 24A shows the locking device 503 in inactivemode, and FIG. 24B shows the locking device 503 in active mode (e.g.,being deployed). The locking device 503 in FIGS. 24A and 24B has an axis561, around which the locking device 503 can rotate. When not activated,the locking device 503 rotates back into the load port supporter 380.When activated, the locking device 503 rotates out of the load portsupporter 380 and locks into position to limit (e.g., stop) the movementof the mask pod 150.

Embodiments may have various advantages. The load port supporter (e.g.,210 in FIGS. 4 and 310 in FIG. 7) increases the effective height of theload port, reduces the lateral movement of the mask pod, and reduces thechance of the reticle getting out of the load port and being damaged.The smart load port design, with sensors embedded, may detect abnormalconditions (e.g., separation of the upper mask pod from the lower maskpod, or non-perpendicular movement of the mask pod) of the mask pod. Thebuilt-in locking devices in the load port supporters may be deployed inresponse to the detection of the abnormal condition to limit themovement of the mask pod, which may prevent or reduce the chance of thereticle getting damaged.

FIG. 25 illustrates a flow chart of a method of operating a load portused in photolithography processing, in accordance with someembodiments. It should be understood that the embodiment method shown inFIG. 25 is merely an example of many possible embodiment methods. One ofordinary skill in the art would recognize many variations, alternatives,and modifications. For example, various steps as illustrated in FIG. 25may be added, removed, replaced, rearranged and repeated

Referring to FIG. 25, at step 1010, a mask pod is lifted up from abottom of the load port, the mask pod carrying a reticle. At step 1020,an abnormal condition of the mask pod is detected. At step 1030, inresponse to detecting the abnormal condition, one or more lockingdevices are activated in the load port to limit movement of the maskpod.

In an embodiment, an apparatus configured to load or unload a mask podincludes a first load port supporter; and a second load port supporterspaced apart from the first load port supporter, where each of the firstload port supporter and the second load port supporter includes at leastportions of an L-shaped rectangular prism, where the first load portsupporter and the second load port supporter are disposed diagonallyaround a rectangular area, where first inner sidewalls of the first loadport supporter and second inner sidewalls of the second load portsupporter delimit boundaries of the rectangular area, and where a firstwidth of the rectangular area is equal to a second width of the maskpod, and a first length of the rectangular area is equal to a secondlength of the mask pod. In an embodiment, the apparatus further includesa load port, where the first load port supporter and the second loadport supporter are attached to a first upper corner of the load port anda second upper corner of the load port, respectively, where the firstupper corner and the second upper corner are two diagonal corners of theload port. In an embodiment, inner sidewalls of the load port are flushwith respective first inner sidewalls of the first load port supporterand flush with respective second inner sidewalls of the second load portsupporter. In an embodiment, the load port has chamfers between an uppersurface of the load port and inner sidewalls of the load port, where thechamfers form a first angle with the upper surface of the load port,where the first load port supporter has a first bottom extension, wherea slanted surface of the first bottom extension forms a second anglewith a bottom surface of the first load port supporter, where the firstangle is equal to the second angle. In an embodiment, the first loadport supporter has chamfers between an upper surface of the first loadport supporter and the first inner sidewalls, and the second load portsupporter has chamfers between an upper surface of the second load portsupporter and the second inner sidewalls. In an embodiment, theapparatus further includes a first pair of optical sensors including afirst optical transmitter and a first optical receiver, the first pairof optical sensors being disposed in a first vertical location of thefirst load port supporter and a first vertical location the second loadport supporter, respectively; a second pair of optical sensors includesa second optical transmitter and a second optical receiver, the secondpair of optical sensors being disposed in a second vertical location ofthe first load port supporter and a second vertical location the secondload port supporter, respectively; and a pair of locking devicescomprising a first locking device and a second locking device, the pairof locking devices being disposed in a third vertical location of thefirst load port supporter and a third vertical location of the secondload port supporter, respectively, where the pair of locking devices arebetween the first pair of optical sensor and the second pair of opticalsensors. In an embodiment, the apparatus further includes a control unitcoupled to the first pair of optical sensors, the second pair of opticalsensors, and the pair of locking devices, where the control unit isconfigured to: based on an output of the first pair of optical sensorsand an output of the second pair of optical sensors, detect separationof an upper mask pod of the mask pod from a lower mask pod of the maskpod while the mask pod is being unloaded; and in response to detectingthe separation of the upper mask pod from the lower mask pod, activatethe pair of locking devices to limit movement of the lower mask pod. Inan embodiment, the first load port supporter and the second load portsupporter have locking devices, where the apparatus further includes: amovable base under the first load port supporter and under the secondload port supporter; a plurality of sensors on an upper surface of themovable base; and a control unit coupled to the plurality of sensors andthe locking devices, where the control unit is configured to: based onoutputs of the plurality of sensors, detect tilting of the mask podduring unloading of the mask pod; and in response to detecting titlingof the mask pod, activate at least one of locking devices to limitmovement of the mask pod. In an embodiment, the plurality of sensorsinclude sensors selected from the group consisting essentially ofpressure sensor, ranger finders, acoustic sensors, current sensors,magnetic sensors, air flow sensors, and liquid flow sensors. In anembodiment, the plurality of sensors comprises a first sensor and asecond sensor, where the control unit is configured to: calculate adifference between a first output of the first sensor and a secondoutput of the second sensor; compare a magnitude of the calculateddifferent with a pre-determined threshold; and determine that titling ofthe mask pod is detected when the magnitude of the calculated differenceis larger than the pre-determined threshold. In an embodiment, theplurality of sensors includes an acoustic transmitter and an acousticreceiver that are configured to measure a traveling time of an acousticwave between the acoustic transmitter and the acoustic receiver, whereinthe control unit is configured to: calculate a difference between themeasured traveling time and an expected traveling time; compare amagnitude of the calculated difference with a pre-determined threshold;and determine that tilting of the mask pod is detected when themagnitude of the calculated difference is larger than the pre-determinedthreshold.

In an embodiment, a load port for loading and unloading a mask podincludes a first load port supporter having a shape of a first L-shapedrectangular prism; and a second load port supporter having a shape of asecond L-shaped rectangular prism, where in a plan view, a first innersidewall of the first load port supporter, a second inner sidewall ofthe first load port supporter, a first inner sidewall of the second loadport supporter, and a second inner sidewall of the second load portsupporter define four different sides of a rectangle, where a dimensionof the rectangle is the same as a dimension of the mask pod; and opticalsensors and locking devices embedded in the load port. In an embodiment,the first load port supporter has beveled edges connecting an uppersurface thereof and the first inner sidewall and the second innersidewall thereof. In an embodiment, a bottom surface of the first loadport supporter and a bottom surface of the second load port supporterare disposed in a first plane, where the optical sensors and the lockingdevices include: a first optical transmitter in the first load portsupporter; a first optical receiver in the second load port supporter,where the first optical transmitter and the first optical receiver are afirst distance away from the first plane; a second optical transmitterin a first one of the first load port supporter and the second load portsupporter; a second optical receiver in a second one of the first loadport supporter and the second load port supporter, where the secondoptical transmitter and the second optical receiver are a seconddistance away from the first plane, the second distance being smallerthan the first distance; a first locking device in the first load portsupporter; and a second locking device in the second load portsupporter, where the first locking device and the second locking deviceare a third distance away from the first plane, where the third distanceis larger than the second distance but smaller than the first distance.In an embodiment, the load port further includes a control unit coupledto a first output of the first optical receiver and coupled to a secondoutput of the second optical receiver, where the control unit isconfigured to, during unloading of a mask pod from the load port: detectthat an upper mask pod of the mask pod is detached from a lower mask podof the mask pod; and in response to detecting that the upper mask pod isdetached from the lower mask pod, deploy at least one of the firstlocking device and the second locking device to limit movement of thelower mask pod. In an embodiment, the load port further includes: afirst locking device in the first load port supporter; a second lockingdevice in the second load port supporter; a movable base having an uppersurface that contacts the first load port supporter and the second loadport supporter during unloading of the mask pod; and a first sensor anda second sensor on the upper surface of the movable base, where thefirst sensor and the second sensor are configured to detect an unevenuplifting of the mask pod.

In an embodiment, a method of operating a load port used inphotolithography processing includes: lifting a mask pod up from abottom of the load port, the mask pod carrying a reticle; detecting anabnormal condition of the mask pod; and in response to detecting theabnormal condition, activating one or more locking devices of the loadport to limit movement of the mask pod. In an embodiment, the abnormalcondition includes a separation of an upper mask pod of the mask podfrom a lower mask pod of the mask pod, where the load port includes afirst pair of optical sensors in sidewalls of the load port, where theload port includes a second pair of optical sensors in the sidewalls ofthe load port and over the first pair of optical sensors, wheredetecting the abnormal condition uses an output from the first pair ofoptical sensors and an output from the second pair of optical sensors.In an embodiment, the abnormal condition includes an uneven uplifting ofthe mask pod, where the load port includes a first sensor and a secondsensor that are on an upper surface of a base of the load port, wheredetecting the abnormal condition includes calculating a differencebetween a first output of the first sensor and a second output of asecond sensor, and comparing a magnitude of the difference to apre-determined threshold. In an embodiment, the load port includes: atleast two pairs of optical sensors disposed along a vertical directionof the load port; at least two sensors disposed along a horizontaldirection of the load port; and a control unit, where the control unitutilizes outputs from the at least two pairs of optical sensors and theat least two sensors to detect the abnormal condition of the mask pod.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. An apparatus configured to load or unload a maskpod, the apparatus comprising: a load port; and a first load portsupporter attached to a first corner of the load port, wherein the firstload port supporter comprises at least portions of an L-shapedrectangular prism and protrudes above an upper surface of the load port.2. The apparatus of claim 1, wherein the load port has a rectangularring shape.
 3. The apparatus of claim 2, wherein the load port haschamfers between the upper surface of the load port and inner sidewallsof the load port.
 4. The apparatus of claim 3, wherein the innersidewalls of the load port are flush with respective inner sidewalls ofthe first load port supporter.
 5. The apparatus of claim 3, wherein thechamfers of the load port form a first angle with the upper surface ofthe load port, wherein a bottom surface of the first load port supportercontacts the upper surface of the load port, wherein the first load portsupporter has a first bottom extension, and a slanted surface of thefirst bottom extension forms a second angle with the bottom surface ofthe first load port supporter, wherein the first angle is the same asthe second angle.
 6. The apparatus of claim 2, further comprising asecond load port supporter attached to a second corner of the load port,wherein the first corner and the second corner are two diagonal cornersof the load port.
 7. The apparatus of claim 1, wherein the first loadport supporter comprises a first material with a first hardness, and theload port comprises a second material with a second hardness, whereinthe first hardness is larger than the second hardness.
 8. The apparatusof claim 1, wherein the first load port supporter comprises an opticalsensor.
 9. The apparatus of claim 8, wherein the first load portsupporter further comprises a locking device.
 10. The apparatus of claim1, further comprising a movable base under the load port, wherein themovable base comprises at least two sensors at an upper surface of themovable base facing the load port.
 11. The apparatus of claim 10,wherein outputs of the two sensors are pressure-sensitive.
 12. A methodof operating a load port for semiconductor manufacturing, the methodcomprising: lifting a mask pod up from a bottom of the load port, themask pod carrying a reticle; detecting an abnormal condition of the maskpod during lifting of the mask pod; and in response to detecting theabnormal condition, limiting movement of the mask pod.
 13. The method ofclaim 12, wherein limiting movement of the mask pod comprises activatinga locking device of the load port to limit movement of the mask pod. 14.The method of claim 13, wherein the locking device protrudes into aspace between opposing inner sidewalls of the load port when activated.15. The method of claim 12, wherein the mask pod comprises an upper maskpod and a lower mask pod, wherein the abnormal condition comprisesseparation of the upper mask pod from the lower mask pod, whereindetecting the abnormal condition comprises: monitoring outputs from twopairs of optional sensors embedded vertically in sidewalls of the loadport; and declaring the abnormal condition when the outputs from the twopairs of optional sensors are abnormal.
 16. The method of claim 12,wherein the abnormal condition comprises an uneven uplifting of the maskpod, wherein detecting the abnormal condition comprises: monitoringoutputs from two sensor disposed at an upper surface of a movable baseof the load port, wherein the mask pod is placed on the upper surface ofthe movable base before being lifted up; calculating a differencebetween the outputs from the two sensors; comparing the calculateddifference with a pre-determined threshold; and declaring the abnormalcondition when the calculated difference is above the pre-determinedthreshold.
 17. A method of operating a load port for semiconductormanufacturing, the method comprising: moving a mask pod along innersidewalls of the load port from a bottom of the load port toward a topof the load port; receiving, by a first optical receiver, a firstoptical signal transmitted by a first optical transmitter; receiving, bya second optical receiver, a second optical signal transmitted by asecond optical transmitter, wherein the first optical transmitter, thesecond optical transmitter, the first optical receiver, and the secondoptical receiver are embedded in the inner sidewalls of the load port,wherein the first optical transmitter and the first optical receiver aredisposed further from the bottom of the load port than the secondoptical transmitter and the second optical receiver; recording, at aplurality of time instants, first values of the first optical signal andsecond values of the second optical signal, wherein each one of thefirst values and a respective one of the second values define a state ofthe first and second optical receivers at a respective time instant; anddetecting, by a control unit, an abnormal condition of the pod mask bydetecting an abnormal state of the first and the second opticalreceivers.
 18. The method of claim 17, further comprising: in responseto detecting the abnormal state, deploying, by the control unit, alocking device to limit movement of the mask pod.
 19. The method ofclaim 17, further comprising: analyzing, by the control unit, a sequenceof the state of the first and second optical receivers; andreconstructing, by the control unit, how and when the abnormal conditionoccurs.
 20. The method of claim 19, wherein the reconstructingcomprises: detecting, by the control unit, transitions in the sequenceof the state of the first and second optical receivers; and determining,by the control unit, time instants of the transitions using time stampsof the recorded first values and the recorded second values.